TAIPEI, Taiwan — The United States unveiled its unofficial embassy in Taiwan’s capital on Tuesday, holding a low-key ceremony that signaled its support for the self-governing island while also trying to avoid a bigger clash with China, which claims Taiwan as its territory.

While Taiwan’s president, Tsai Ing-wen, and her predecessor both attended the dedication of the new, $250 million compound of the American Institute in Taiwan, the highest-ranking attendee from Washington was Marie Royce, the assistant secretary of state for educational and cultural affairs.

James Moriarty, the chairman of the Virginia-based headquarters of the institute, and Representative Gregg Harper, a Republican from Mississippi, were also part of the American delegation.

The institute, known as the A.I.T., serves as the de facto embassy for the United States, which broke off formal diplomatic relations with Taiwan when it switched recognition to the Communist government in Beijing in 1979.

There had been speculation that President Trump might make a bolder show of support for Taiwan, which has emerged as one of the most vibrant democracies in Asia. However, the lack of cabinet-level visitors from Washington displayed the Trump administration’s unwillingness to upset China, with whom it is already locked in a standoff over trade.

Mr. Trump has also sought China’s help in arranging the landmark summit meeting that took place on Tuesday in Singapore between Mr. Trump and the North Korean leader, Kim Jong-un. That meeting deflected American and global attention away from the institute’s dedication.

As in the case of the summit meeting on the other side of the South China Sea, China was not present, but was certainly watching. The government in Beijing views Taiwan as its sovereign territory, which it has vowed to reclaim by force if necessary, despite never having actually ruled the island.

At a regular media briefing in Beijing, a Foreign Ministry spokesman, Geng Shuang, said the ceremony “will have a negative impact” on China’s ties with the United States. “We are having very serious discussions now, and any participation of U.S. officials in Taiwan-related events or activities is violating agreements between the U.S. and China.”

Rumors had run rampant here for months that the Trump administration might send a higher-profile visitor to make a more open show of support for Taiwan, which has faced increasing military and diplomatic pressure from China.

In a show of how important the American presence is for Taiwan, the island’s president, Ms. Tsai, was joined at the dedication ceremony by her predecessor, Ma Ying-jeou. Many of Taiwan’s top politicians sat in the audience of about 200.

“As we dedicate this building, we also rededicate ourselves to our common sense of purpose,” Ms. Tsai said. “As free and open democracies, we have an obligation to work with one another to defend our values and protect our joint interests.”

When asked by a journalist if he was disappointed that no higher-level representatives were sent from Washington, Mr. Moriarty, the institute’s chairman, pointed to the summit meeting in Singapore.

“I believe there is a lot going on in the region today, and we need to respect that,” he said.

Speaking to a crowd of reporters before the ceremony, the institute’s director, Kin Moy, a career diplomat in the State Department, said the new building’s unveiling showed Washington’s “unshakable” commitment to Taiwan.

After delays since its groundbreaking in 2009, the institute’s fortified compound on the northern edge of Taipei, Taiwan’s capital, will begin operations in September, when some 450 staff members, including several American diplomats, will relocate from their current offices scattered around the city.

The institute performs most of the same functions as an embassy, including issuing visas. It is the largest diplomatic mission — official or unofficial — in Taiwan, making it a symbol of both Taiwan’s awkward diplomatic limbo and also its quiet but strong ties with the United States.

American support for Taiwan goes back to the end of China’s civil war in 1949, when Chiang Kai-shek, the World War II ally of the United States, fled to the island with his Republic of China government after being routed by Mao Zedong’s Communists.

The lack of mutual recognition between the governments in Beijing and Taipei and Beijing’s insistence on treating Taiwan as its own territory have created a situation in which other countries are forced to recognize either China or Taiwan, but not both. Only a handful of nations, mostly in the Pacific and the Caribbean, keep formal embassies in Taiwan, which still calls itself the Republic of China.

While tiny Taiwan no longer poses a military threat to China, its status as a Chinese-speaking democracy is viewed as an ideological threat by Beijing’s authoritarian government. Calls for absorbing Taiwan have grown steadily louder under Xi Jinping, China’s strongest leader since Mao.

Taiwan’s freedom of speech was on display outside of the institute’s dedication ceremony. While security was tight inside, rival demonstrators vied for attention outside the building’s gates. One group advocated scrapping the Republic of China in favor of a new country called Taiwan. Across the street, a smaller group raised banners calling for unification with China.

Elsie Chen contributed research from Beijing.

A version of this article appears in print on , on Page A6 of the New York edition with the headline: U.S. Avoids Irking China In Opening Taiwan Office. Order Reprints | Today’s Paper | Subscribe